Droplet microfluidics has shown promise in recent years in a range of chemical and biological applications (Whitesides, G. M. Nature 2006, 442, 368-373; Song, H.; Chen, D. L.; Ismagilov, R. F. Angew. Chem. Int. Ed. 2006, 45, 7336-7356; Huebner, A.; Sharma, S.; Srisa-art, M.; Hollfelder, F.; Edel, J. B.; Demello, A. J. Lab chip 2008, 8, 1244-1254; Liu, D.; Wang, S. Chem. Eng. Proc. 2008, 47, 2098-2106; Liu, D.; Zhang, J.; Li, D.; Kong, Q.; Zhang, T.; Wang, S. AIChE J. 2009, 55, 726-736; Chiu, D. T.; Lorenz, R. M. Acc. Chem. Res. 2009, 42, 649-658; Therberge, A. B.; Courtois, F.; Schaerli, Y.; Fischlechner, M.; Abell, C.; Hollfelder, F.; Huck, W. T. S. Angew. Chem. Int. Ed. 2010, 49, 5846-5868; Bai, Y.; He, X.; Liu, D.; Patil, S. N.; Bratton, D.; Huebner, A.; Hollfelder, F.; Abell, C.; Huck, W. T. S. Lab Chip 2010, 10, 1281-1285; Chiu, D. T. Anal. Bioanal. Chem. 2010, 397, 3179-3183; Liu, D.; Wang, S. Ind. Eng. Chem. Res. 2011, 50, 2323-2330; Anna, S. L.; Bontoux, N.; Stone, H. A.; Appl. Phys. Lett. 2003, 82, 364-366; Thorsen, T.; Roberts, R. W.; Arnold, F. H.; Quake, S. R. Phys. Rev. Lett. 2001, 86, 4163-4166). A small sub-area of droplet microfluidics has been focused on the formation of double emulsions, which are droplets of dispersed phase containing even smaller droplets within. Double emulsions are found in diverse areas, from food, cosmetics, to pharmaceutics (Edris, A.; Bergnstahl, B. Food/Nahrung. 2001, 45, 133-137; Engel, R. H.; Riggi, S. J.; Fahrenbach, M. J. Nature 1968, 219, 856-857; Lee, M.; Oh, S.; Moon, S.; Bae, S. J. Colloid Interface Sci. 2001, 240, 83-89).
Microfluidics approaches have been devised for producing double emulsions in the condensed phase (Abate, A. R.; Weitz, D. A. Small 2009, 5, 2030-2032; Utada, A. S.; Lorenceau, E.; Link, D. R.; Kaplan, P. D.; Stone, H. A.; Weitz, D. A. Science 2005, 308, 537-541; Okushina, S.; Nisisako, T.; Torii, T.; Higuchi, T. Langmuir 2004, 20, 9905-9908; Bauer, W. C.; Fischlechner, M.; Abell, C.; Huck, W. T. S. Lab chip 2010, 10, 1814-1819), however, a variety of applications for the use of double emulsions remain unexplored. For example, there is a need to introduce double emulsions and other droplets into analytical instruments, such as gas chromatographs.